Creating a custom analyzer in ElasticSearch Nest client

Question

Im very very new to elasticsearch using the nest client, I am creating an index with a custom analyzer, however when testing using analyze it does not seem to use the custom analyzer. Mainly no edgengram tokens appear. Is there anything I am missing that would make my custom analyser the default for the index? When I check my mappings using elastichq they show my custom analyzer.

ConnectionSettings settings = new ConnectionSettings(new Uri("http://localhost:9200"),    defaultIndex: "forum-app");

 IndexSettings indsettings = new IndexSettings();

   var an = new CustomAnalyzer();

   an.CharFilter = new List<string>();
   an.CharFilter.Add("html_strip");
   an.Tokenizer = "edgeNGram";
   an.Filter = new List<string>();
   an.Filter.Add("standard");
   an.Filter.Add("lowercase");
   an.Filter.Add("stop");

indsettings.Analysis.Tokenizers.Add("edgeNGram", new Nest.EdgeNGramTokenizer
{
    MaxGram = 15,
    MinGram = 3
});

indsettings.Analysis.Analyzers.Add("forumanalyzer", an);

ElasticClient client = new ElasticClient(settings);

client.CreateIndex("forum-app", c => c
.NumberOfReplicas(0)
.NumberOfShards(1)
.AddMapping<Forum>(e => e.MapFromAttributes())
.Analysis(analysis => analysis
.Analyzers(a => a
.Add("forumanalyzer", an) 
)));        

//To index I just do this       
client.Index(aForum);

I got NullReferenceException trying to use your code. Analysis property is null. That why I can't add my custom analyzer to the Analyzers. Did you have that problem? @yaly_cu — Joseph Katzman
– Joseph Katzman, Commented Feb 2, 2017 at 12:36

Greg Marzouka · Accepted Answer · 2014-08-09 14:41:25Z

You've added your custom analyzer to your index, but now you need to apply it your fields. You can do this on a field mapping level:

client.CreateIndex("forum-app", c => c
    .NumberOfReplicas(0)
    .NumberOfShards(1)
    .AddMapping<Forum>(e => e
        .MapFromAttributes()
        .Properties(p => p
            .String(s => s.Name(f => f.SomeProperty).Analyzer("formanalyzer")))
    )
    .Analysis(analysis => analysis
        .Analyzers(a => a
            .Add("forumanalyzer", an)
        )
    )
);

Or you can apply it to all fields by default by setting it as the default analyzer of your index:

client.CreateIndex("forum-app", c => c
    .NumberOfReplicas(0)
    .NumberOfShards(1)
    .AddMapping<Forum>(e => e.MapFromAttributes())
    .Analysis(analysis => analysis
        .Analyzers(a => a
            .Add("default", an)
        )
    )
);

More info here in regards to analyzer defaults.

ttt · Accepted Answer · 2018-05-16 09:50:28Z

Add a custom analyzer:

var indexSettings = new IndexSettings
{
    NumberOfReplicas = 0, // If this is set to 1 or more, then the index becomes yellow.
    NumberOfShards = 5
};

indexSettings.Analysis = new Analysis();
indexSettings.Analysis.Analyzers = new Analyzers();
indexSettings.Analysis.TokenFilters = new TokenFilters();

var customAnalyzer = new CustomAnalyzer
{
    //CharFilter = new List<string> { "mapping " }, 
    Tokenizer = "standard",
    Filter = new List<string> { "lowercase", "asciifolding" }
};

indexSettings.Analysis.Analyzers.Add("customAnalyzerLowercaseSynonymAsciifolding", customAnalyzer);

And then when creating the index, you specify the analyzer:

var indexConfig = new IndexState
{
    Settings = indexSettings
};

 var createIndexResponse = elasticClient.CreateIndex(indexName, c => c
   .InitializeUsing(indexConfig)
   .Mappings(m => m
       .Map<ElasticsearchModel>(mm => mm
           .Properties(
           p => p
           .Text(t => t.Name(elasticsearchModel => elasticsearchModel.StringTest).Analyzer("customAnalyzerLowercaseSynonymAsciifolding"))                          
           )
       )
   )
);

elasticClient.Refresh(indexName);

And then you query it with something like:

var response = elasticClient.Search<ElasticsearchModel>(s => s
        .Index(indexName)
        .Query(q => q
              .SimpleQueryString(qs => qs
                  .Fields(fs => fs
                       .Field(f => f.StringTest, 4.00)
                  )
                  .Query(query)
                 )
               )
           );

var results = new List<ElasticsearchModel>();
results = response.Hits.Select(hit => hit.Source).ToList();

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